The contribution of genomic silencing to tumorigenesis through genetic mutation, deletions, or epigenetic alterations has been increasingly recognized in a variety of human malignancies, including chronic lymphocytic leukemia (CLL). Epigenetic modifications, including DNA methylation and histone acetylation, appear to be much more common in B-cell malignancies than mutations or deletions, and are readily reversible by targeted therapeutic interventions. Extensive preliminary data has demonstrated that inhibition of DNA methyltransferase (DNA MeT) and histone deacetylase (HDAC) can lead to re-expression of silenced genes and selective cytotoxicity of CLL cells in vitro. The specific aims of this proposal are 1) To determine the minimally effective pharmacologic dose (MEPD) of the DNA MeT inhibitor, decitabine, in combination with the HDAC inhibitor, valproic acid, in patients with fludarabine-refractory CLL, 2) To attain an understanding of the conduction and interpretation of detailed pharmacokinetic and pharmacodynamic assays performed as part of the MEPD-finding study of decitabine and valproic acid described in Aim 1, and 3) To perform a phase I trial using a novel schedule of the HDAC inhibitor, depsipeptide, with in vivo evaluation of HDAC enzyme inhibition and CD20, CD80, CD86, HLA-DR, and c-FLIP expression. The detailed phase I trials outlined in these aims will provide the applicant with a thorough education in the conduction of early clinical trials supported by biologic endpoints and translational research. The extensive pharmacokinetic and pharmacodynamic analyses will validate in vivo the DNA MeT depletion, HDAC enzyme inhibition, histone H3 and H4 acetylation, and gene re-expression assays, permitting later expansion of this work to B-cell non-Hodgkin's lymphoma. The wealth of scientific expertise regarding epigenetic modifications in human malignancies available at The Ohio State University, the mentorship of Drs. John Byrd and Michael Grever, recognized leaders in CLL pathogenesis and therapy, and the mentorship of Dr. Christoph Plass, an expert in aberrant DNA methylation in human malignancies, will ensure the success of this proposal. With the support of this grant, the applicant will perform the previously described phase I trials and participate in formal didactic clinical investigator training through a NIH K30- funded Clinical Research Curriculum available at The Ohio State University, with the long-term goal of becoming an independently funded clinical investigator.